Evaluating the Effects of Threadfin Shad on Largemouth Bass and Bluegill Populations in Small Impoundments

Abstract

Threadfin Shad are commonly stocked into small impoundments (<40 hectares in surface area) to increase the growth and condition of Largemouth Bass, ultimately to enhance recreational fishing. However, the effects of Threadfin Shad on Largemouth Bass and Bluegill growth and condition in small impoundments are not fully understood. To date, much Threadfin Shad research has focused on large reservoirs with few studies conducted on small impoundments. With over 250,000 small impoundments in Alabama alone, understanding the role of Threadfin Shad in these systems is paramount to providing the best management advice. We evaluated the impacts of Threadfin Shad on Largemouth Bass growth, condition, and diets and Bluegill growth and condition at five recently-stocked and 29 established small impoundments in central Alabama. Results from this study suggest that Threadfin Shad increase the initial growth of Largemouth Bass but do not have significant impacts on Largemouth Bass condition. Largemouth Bass in impoundments recently established impoundments fed primarily on Threadfin Shad whereas Largemouth Bass in established impoundments fed primarily on Bluegill and only supplemented their diet with Threadfin Shad. Threadfin Shad were associated with drastic declines in zooplankton density, low larval Bluegill densities, and low seine catches of age-0 Bluegill in the littoral zone. Bluegill condition was lower in established but not in recently established impoundments. Bluegill growth was not affected by the presence of Threadfin Shad. Results of this study will provide a better understanding of interactions between Threadfin Shad and Largemouth Bass and Bluegill and provide managers with insight on how to better manage small impoundments.